According to a study by Imperial College London, the risk of reinfection with the Omicron variant is over 5-fold higher and seems to be no milder than the Delta variant.

On the basis of data from the UK Health Security Agency and National Health Service on people who tested COVID-positive in England from November 29 to December 11, researchers stated that there appears to be no evidence, for both hospitalization risk and symptom status, that Omicron has different severity compared to Delta variant. However, the study stated that data on hospitalizations is very limited. After controlling for vaccine status, age, sex, ethnicity, region, asymptomatic status, and specimen date, the Omicron variant was found to be tied to a 5.4-fold greater risk of reinfection in comparison with the Delta variant. This indicates that the protection against reinfection with Omicron variant conferred by prior COVID-19 infection may be only 19%, stated Imperial College… (NDTV – Reuters, December 17, 2021)